1. Field of the Invention
The present invention relates generally to a cooling device for semiconductor elements that emit a substantial quantity of heat and, in particular but not exclusively, to a compact, easy to handle and efficient cooling device for cooling semiconductor elements by utilization of a change in phase between a liquid phase and a vapor phase of a refrigerant.
2. Description of the Related Art
It is well known that some of the semiconductor elements used in, for example, a computer emit a substantial quantity of heat as the computing speed thereof increases. A cooling device including a fan and a heat sink is generally utilized to cool the semiconductor elements. However, the capability of the air-cooling device to cool the semiconductor elements has now come to limitations.
In the case of a large scale computer, a relatively complicated cooling device is employed which includes a specially designed multi-layered ceramic wiring substrate and a housing mounted on the wiring substrate to define a cavity therein for accommodating a quantity of refrigerant, as disclosed in, for example, Japanese Laid-open Patent Publication No. 5-136305 published Jun. 1, 1993. The semiconductor elements are, while they are immersed in the refrigerant within the cavity, cooled in contact with the refrigerant. This cooling device dedicated for use with a large scale computer is indeed not suited for general use.
On the other hand, Japanese Laid-open Patent. Publication No. 6-120382 published Apr. 28, 1994 suggests a compact cooling device of a heat-pipe type operable by utilization of the phase change of a refrigerant used. This heat-pipe type cooling device would involve an increase in size and/or insufficient cooling performance particularly when it is used in cooling highly exothermic semiconductor elements.
In any event, the cooling device utilizing the fan and the heat sink is generally used in cooling elements that emit a relatively small quantity of heat.
With the conventional air-cooling device utilizing the fan and the heat sink, it is possible to construct a cooling device effective to cool semiconductor elements of about 70 W. When it comes to cooling of semiconductor elements of 150 W or higher, the cooling device tends to become extremely bulky or too bulky for it to be incorporated within a frame structure or the like. On the other hand, the system in which the semiconductor elements are immersed in the refrigerant such as disclosed in Japanese Laid-open Patent Publication No. 5-136305 discussed above, has a problem associated with the sealing properties of a vessel for accommodating the semiconductor elements to be cooled and also a problem associated with a storage capability and handing properties because of the cooling device complicated in structure.
In view of the foregoing, the present invention is devised to eliminate the problems hereinabove discussed and is intended to provide a compact cooling device capable of efficiently cooling highly exothermic semiconductor elements.
In accomplishing the above and other objectives, the present invention provides a cooling device for cooling a semiconductor element, which includes at least one cold plate utilizing a copper plate for cooling the semiconductor element, a condenser utilizing a plurality of flat micro-tubes, a refrigerant pump for circulating a refrigerant, and a fan for cooling the condenser. The cold plate, the condenser, and the refrigerant pump are fluid connected to define a refrigerant circulating circuit.
According to the present invention, the refrigerant condensed by the condenser is supplied by the refrigerant pump towards the cold plate which in turn cool the semiconductor element that is mounted on, or otherwise held in contact with the cold plate. Specifically, the cold plate with the refrigerant flowing therethrough absorbs heat emitted from the semiconductor element, causing the refrigerant to undergo a change in phase from a liquid refrigerant to a vapor refrigerant before it is returned to the condenser. The fan fitted to the condenser allows heat of the vapor refrigerant to be absorbed to cause the refrigerant to undergo a change in phase from the vapor refrigerant to the liquid refrigerant. The use of an efficient flat micro-tube condenser for the condenser and the use of an efficient copper plate for the cold plate make it possible to manufacture an efficient and compact cooling device.
In a preferred embodiment of the present invention, the plurality of flat micro-tubes are arranged such that a refrigerant supplied from the cold plate enters one of the flat micro-tubes positioned remote from the fan and emerges outwardly from another flat micro-tube positioned close to the fan. This allows a desirable temperature difference between the refrigerant and an air current induced by the fan to be efficiently obtained in each of the rows of the flat micro-tubes forming the condenser, resulting in highly efficient heat exchange.
Advantageously, an inlet through which the refrigerant enters the condenser is defined at a high position and an outlet through which the refrigerant emerges outwardly from the condenser is defined at a lower potion than the high position for the inlet. With this feature, the liquid refrigerant and the vapor refrigerant can be uniformly distributed to and flow through the plurality of flat micro-tubes, making it possible to maximize utilization of the flat micro-tube condenser. Since only the liquid refrigerant is discharged from the outlet of the condenser, not only can reduction of the flow, which would result from an entrapment of the gas by the refrigerant pump, be avoided, but a stable cooling performance can be also obtained.
It is preferred that a plurality of cold plates be employed which are fluid connected in series with each other. According to this feature, a plurality of semiconductor elements can be cooled in sequence determined by the order of arrangement of the cold plates and, hence, the semiconductor elements even though they emit different quantities of heat can satisfactorily be cooled, making it possible to suppress an undesirable increase of temperature of the semiconductor elements.
Conveniently, the cold plate has a plurality of fluid passages defined therein, all of which are fluid connected in series with each other by at least one copper tube for passage of the refrigerant therethrough. With this feature, the cold plate can be made merely by soldering the copper tube to the cold plate.
Alternatively, the cold plate may have a flat cavity defined therein, through which the refrigerant flow. With this feature, the surface area of contact of the refrigerant within the cavity with the copper plate can be increased, thus achieving highly efficient cooling.